1. Field of the Invention
This invention relates to a scanning apparatus, and more particularly to a scanning apparatus being able to scan both transparent and reflective objects.
2. Description of Prior Art
With the increasing widespread of computers and the Internet, more image data is utilized in hypertext documents. Therefore, scanners are very popular. There are various ways to input video data to a computer, for example with digital cameras and scanners, etc. But a scanner is the best choice for inputting images of flat documents such as photographs or slides, etc.
A conventional scanner is generally a reflective scanner. That is, its light source and the image detector are located at the same side of the document to be scanned. Therefore, it can only scan opaque documents, not a film or a slide.
To address this question, various scanners have been provided that is able to scan a transparent document. Referring to FIG. 1, Taiwanese patent application number No. 85213005 provides two sets of light sources 10, 12 to respectively scan a reflective document and a transparent document. Then a revolvable mirror 14 is used to choose one of the light sources to project to the image recording device 18 after passing through reflective mirrors and lens set 16. In this prior art, two sets of light sources 10, 12 and a revolvable mirror 14 are used to choose different light paths. It has a complex structure; thus its cost is relatively high.
To address this weakness, several prior arts can scan both reflective and transparent objects have been developed. Referring to FIG. 2a, Taiwanese patent application No. 85218816 provides a revolving apparatus 20 to enable the light source 22 to switch between particular positions at both sides of the glass plate 24 holding documents to be scanned. Thus, the scanner can scan a reflective object when the light source 22 and image convert device 26 are located at the same side to the glass plate 24, otherwise the scanner can scan a transparent object. However, in order to allow the glass plate 24 to move across the supporting mechanism 20, the mechanism 20 for supporting the light source 22 must be wider than the glass plate 24. Hence the structure of such scanner becomes larger. Referring to FIG. 2b, the U.S. Pat. No. 5,907,411 has disclosed a scanner mechanical structure with a reflective scanning platform 27 and a transparent scanning platform 29. However, two light sources are used for reflective scanning and transparent scanning respectively.
To avoid the problems mentioned above, another scanner using only one light source to scan documents is disclosed. Referring to FIG. 3, in Taiwanese patent application No. 86200497, the light produced by the light source 30 is divided to respectively scan a reflective object 32 and scan a transparent object 34. Different optical components are used to transmit the images of the reflective object 32 and scan the transparent object 34 respectively to a beam splitter 36. Thus the images coming from different optical paths can be transmitted to an image retrieving apparatus 38 by means of the beam splitter 36. However, a mask 39 has to be used to allow only one of the images being transmitted to the image retrieving apparatus 38 at a time. In this prior art, the scanner has a larger volume since it must use more components.
Accordingly, to address the drawbacks of the prior arts, the object of this invention is to provide an apparatus for scanning both reflective and transparent objects, which uses only one fixed light source to provide an optical path able to respectively scan both a reflective object and a transparent object.
According to the invention, only one set of optical components is needed to scan both a reflective object and a transparent object since there is only one optical path to be used. A reduced number of optical components are used in this scanning apparatus, thus lowering the cost and lessening the physical volume of the scanner.
To attain the above purpose, the invention moves the position of the image-retrieving device to switch the work position of the lens in the image-retrieving device, so that both the image of a reflective object and the image of a transparent object can be precisely formed at an appropriate position.